Cassian Elwes, who spent much of the New York to Los Angeles flight next to a man he identifies as Marco, describes how he tried to keep the man calm as the plane was diverted to Denver.

His account paints a sympathetic portrait of a troubled former marine who was apparently receiving treatment for a psychological disorder.

Cellphone footage shows the man being escorted from the plane at Denver in handcuffs. Video footage obtained by ABC7 also showed the man being escorted from the plane.

"I want to write this all down before I forget it even though its 3.45am," Elwes wrote on Twitter on Monday morning, referring to Pacific time. "I just got home. Tonight I took the 9pm jet blue from ny to lax."

What followed was a gripping blow-by-blow account of the ordeal, posted over a two-hour period.

Hey that's my seat man I said. A quick drawling fuck you its mine now was the response I sat down next to him mumbling 'charming'.

Elwes took the seat next to the man, but then moved to the row directly behind to allow a couple to sit next to one another. It was around an hour into the flight when the man began to behave oddly, according to Elwes.

Elwes, concerned, asks if there is an air marshal onboard but is told that they cannot identify themselves. An air steward calls the captain, however, and learns that there is another off-duty marshal on the plane.

He sits down next to hoodie and they exchange a few words. I'm right behind and now hoodie starts shouting at the guy fuck you many times

As the man's behaviour continued, the air stewards asked passengers if anyone would volunteer to sit next to the individual. Elwes said the off-duty air marshall had by now taken the aisle seat, leaving the middle one free, with the couple unwilling to return.

Elwes, who said he was "feeling quite guilty for switching with the japanese couple in the first place", volunteered to sit next to the man.

Elwes said a woman passenger accused Marco of groping her on the plane and said she would press charges. Elwes also gave a statement to police in Denver before the plane continued onto Los Angeles. "I write that I used to be william morris agent and I've dealt with difficult people before and really this guy wasn't that difficult," he said, but is left reflecting on what will become of him.

I realize the point is these wars are fucking with our children's minds. A whole generation is being sent home screwed up.

Elwes added that he found one of Marco's pills on the floor. With the help of a fellow passenger he discovered that it is a drug used to treat "bi-polar anxiety".

During their conversation Elwes had asked Marco to write down his email address, after Marco said his story should be made into a movie. With Marco escorted off the plane, repeatedly asking Elwes not to forget him as he left, Elwes said he opened the piece of paper to find a note.